<!DOCTYPE html>
<html lang="en">
<head>
	<meta charset="UTF-8">
	<title>圆</title>
</head>
<body>
	半径：<input type="text" placeholder="半径" id="a"><br>周长：<input type="text" placeholder="周长" id="b"><br>面积：<input type="text" placeholder="面积" id="c">
	<script>
		var r = prompt("输入半径(cm)");
		r = Number(r);
  		var p = Math.PI;
  		document.querySelector('#a').value= r+"cm";
  		document.querySelector('#b').value= r*2*p+"cm";
  		document.querySelector('#c').value=r*r*p+"cm²";
	</script>
</body>

</html>